This invention relates to method and apparatus for reaming or enlarging earth bore diameters; and more particularly relates to a novel and improved method and apparatus for cutting through a productive downhole formation to form a well bore diameter substantially larger than a conventionally drilled well bore in order to increase production rates.
In the recovery of petroleum or other gas or liquid substances from subterranean formations, a well bore is formed into the earth and into or beyond the producing formation. A productive well bore is then "completed" either by conventional "cased hole" or "open hole" completion.
In conventional cased hole completion, the casing is run into the completed well bore through and beyond the productive formation after which the casing is cemented in place and then perforated to provide communication between the producing formation and the interior of the casing. Conventional perforations form holes in the casing approximately 3/8" in diameter and the perforation projectile travels a distance of a few inches to a few feet into the formation. Conventional wells typically have one or more perforations per foot.
In conventional open hole completion, the well bore is drilled into the top portion of the productive formation and casing is run to the top of the productive formation and cemented in place. The well bore is then deepened through the productive formation and left open to communicate with the interior of the well bore. Generally, this method establishes more communication with the well bore than a conventional cased hole. The types of completion described are somewhat effective in formations with high permeability. However, with the recent increased number of well completions in formations having low permeability, low production flow rates have resulted with long economic payout periods and unsatisfactory rates of return on investment. The reserves in place may be substantial, but the production flow rates are usually unsatisfactory. The conventional types of completion described provide insufficient productive formation surface area open to communicate with the well bore. Many of the producing formations of these wells are several feet to several hundred feet thick and friable yet structurally strong enough not to collapse when open hole completed.
In the past, many conventional well completions have included various flow rate enhancement treatments including chemical treatments, fracture proppant treatments, horizontal drilling and combinations thereof. Nevertheless, conventional open hole and cased hole completions and subsequent treatments have suffered from numerous drawbacks including:
(a) the surface area of productive formation open to communicate with the interior of the well bore is marginal; PA1 (b) the introduction of foreign treatment chemicals to the formation often chemically alters the formation, activating clays and other flow restricting minerals; PA1 (c) the proppants often break down from formation pressure and create fines which restricts production flow; PA1 (d) the proppant fracture treatments fill the well bore with unwanted proppant precluding installation of downhole production equipment. An expensive workover rig capable of removing the proppant out of the well bore must be employed; PA1 (e) the polymer gels used to assist the proppant into the induced fractures do not entirely break down to a retrievable fluid which restricts production flow; PA1 (f) the chemical or proppant treatments are not controllable as to where they propagate. Neighboring zones containing unwanted production such as salt water are often fractured into and then the unwanted production cannot be stopped; PA1 (g) the chemical and/or proppant may be placed in the induced fractures and yet be squeezed off at any point in the fracture area and especially near the well bore making the proppant ineffective; PA1 (h) the desired production becomes mixed and contaminated with the foreign treatment liquids, gases or solids and are expensive to extract; PA1 (i) the contaminated production postpones initial production revenues; PA1 (j) the contaminated gas production is often vented to atmosphere and contaminated liquid production often incorrectly disposed of causing environmental contamination; PA1 (k) the mixing of treatment chemicals with formation solids, liquids and gases often forms corrosives that corrode production equipment and pipelines; PA1 (l) the horizontal drilling requires an expensive and complicated downhole directional drilling tool and still provides only a marginal increase in the productive formation surface area open to communicate with the well bore; PA1 (m) the chemicals and acids used are a human health hazard and when not properly handled cause serious accidents; PA1 (n) the foreign treatment proppants cause scoring damage and blockage to pumping equipment; PA1 (o) the chemical and proppant fracture treatments require additional equipment, such as, frac tanks, sand and/or chemical trucks, and pumping trucks which cause additional damage to the landowner's surface; PA1 (p) the oil and natural gas purchasers and pipeline companies will not allow numerous fracture treatment gases and liquids in the production because it lowers its heating value; and PA1 (q) the initial flow rate tests are inaccurate due to flow back of treatment fluids and treatment gases.
It is therefore desirable to provide for a method and apparatus for substantially increasing the surface area of the productive formation in such a way as to result in substantially increased production rates and to overcome the numerous problems and drawbacks inherent in conventional open hole and cased hole completions as well as subsequent enhancement treatments. In particular, it is proposed to employ a novel and improved reaming device for enlarging a well bore diameter at the productive formation which is characterized by its ease of installation, operation, versatility and reliability in use.
Representative reaming tools are disclosed in U.S. Pat. Nos. 54,144 to Hamar, 639,036 to Heald, 1,189,560 to Gondos, 1,285,347 to Otto, 1,467,480 to Hogue and 1,485,615 to Jones. Although these devices generally disclose the concept of utilizing one or more pivotal cutters which will swing outwardly under centrifugal force into cutting engagement with the sides of a hole, they are lacking in any suggestion of utilizing flat rigid cutter blades which are capable of swinging outwardly from a position in which the blades are disposed in overlapping relation to one another to a perpendicular position to the rotational axis and which will afford adequate relief for the removal of formation cuttings as the cutter blades are rotated.